The present invention is directed to the preparation of 2-vinylnaphthalenes. The 2-vinylnaphthalenes have use as monomers in the production of vinylnaphthalene polymeric materials.
One route proposed for the preparation of 2-vinylnaphthalene begins with the hydrogenation of 2-acetonaphthalene and subsequent dehydration of the formed 2-methylnaphthyl carbinol. The reaction mechanism which has been proposed is as follows: ##STR1##
Unfortunately, 2-acetonaphthalene is relatively expensive in the pure form due to the poor selectivity which is achieved in acetylating naphthalene to the 2-isomer and in view of the yield loss which is incurred in separating the 2-acetonaphthalene from the 1-isomer.
It is possible to obtain vinylnaphthalene by dehydrogenating ethyl naphthalene. As simple as this process appears, however, it is complicated by the difficulty of recovering the vinylnaphthalene from the reaction mixture. The vinylnaphthalene so readily polymerizes that it is difficult to separate vinylnaphthalene from the unchanged ethyl naphthalene by distillation. A proposed route to forming vinylnaphthalene from ethyl naphthalene is disclosed in U.S. Pat. No. 2,468,759. As disclosed therein, a mixture of 1- and 2-ethyl naphthalene is oxidized to a mixture of methylnaphthyl carbinol and methylnaphthyl ketone. The methylnaphthyl ketone is hydrogenated to methylnaphthyl carbinol and the methylnaphthyl carbinol dehydrated to vinyl naphthalene. The process involves at least three steps in addition to obtaining the starting ethyl naphthalene.
It would appear, however, that a key step in producing pure 2-vinylnaphthalene by the process as disclosed in the patent would become the separation from any coproduced 1-vinylnaphthalene. The patent is silent as to the isomers produced.
Accordingly, it is an object of the present invention to provide an improved process for the production of 2-vinylnaphthalenes which is more economical than previously proposed.